Influence mechanism of solidification mode on solidification cracking susceptibility of stainless steel

It is well-known that the solidification cracking susceptibility of stainless steel changes depending on the amount of ferrite in the weld metal at room temperature. However, the cause and effect of the amount of ferrite at room temperature and solidification cracking have not always been clarified. When considering the temperature range in which solidification cracks occur, it must be necessary to focus on changes in microstructure and behavior during solidification. In this study, the solidification cracking susceptibility of stainless steel was investigated according to the above reasons, and its susceptibility was summarized using the solidification mode, in other words, an amount of delta ferrite during solidification. A quenched microstructure at the solid-liquid coexistence region was obtained for each stainless steel, and the solidification mode and the amount of the delta ferrite during solidification were investigated. The solidification cracking susceptibility was evaluated using the Trans-Varestraint test, and the effect of solidification mode on the brittle temperature range (BTR) was clarified. In addition, a theoretical study on BTR was conducted, and the effect of solidification mode on solidification segregation at each stainless steel was considered. It was found that the solidification segregation behavior changes depending on the solidification mode. Especially, the effect of solidification and segregation of impurity elements such as sulfur and phosphorus were large in the austenite, in the case of ferrite, the carbon was affected by BTR more than the impurity element compared with the austenite. Thus, it has been suggested that the BTR changes due to the solidification segregation of solute elements according to each solidification mode.